Articulated concrete joint member

ABSTRACT

An articulated concrete joint member ( 1 ) including a resilient core ( 2 ), the core ( 2 ) having connections means ( 3 ) attached thereto, the connection means ( 3 ) adapted to link two co-planar concrete slabs ( 5, 6 ) along an adjacent peripheral edge of each slab, wherein on application of an out-of-plane displacement to one of the co-planar concrete slabs ( 5, 6 ) the displacement is transmitted to the other slab through pivoting about the articulated joint member ( 1 ). In one embodiment, the articulated concrete joint member ( 1 ), which further includes crack propagation means ( 4 ), is fully immersed in the concrete slab so that the slab is subjected to extraneous loads, the slab cracks along predetermined lines of weakness ( 7 ).

FIELD OF THE INVENTION

[0001] The invention relates to the construction of pavements andconcrete slabs, and in particular, the jointing method used in cases ofdifferential movement between said slabs.

BACKGROUND OF THE INVENTION

[0002] Pedestrian thoroughfares whether associated with a road, througha park or other means, and which fall under the control and maintenanceresponsibility of a Municipal Council will often be formed fromconcrete. As such pedestrian thoroughfares carry very light trafficloads, typically, such thoroughfares or footpaths will have little or noreinforcement within the concrete.

[0003] Typically, the footpath will be formed from pavement slabs whichare cast in place in significant lengths so as to economically place thepavement by limiting the number of concrete pours required whenconstructing the thoroughfare between locations.

[0004] As the pavement is cast in a unitary mass it is recognized thatthe unitary slab will eventually crack as a result of external factorsand the lack of reinforcement. Such external factors can be rootintrusion from nearby trees, soil heave from saturated expansive clays,soil shrinkage through drying during summer, or differential settlementof the foundation as a result of a poorly prepared base coursesupporting the pavement.

[0005] So as to control the number and placement of this cracking,transverse lines of weakness are placed in the concrete prior to curing.Typically, this is done by trowelling a line across the concrete, andthus provide a localised weakening of the concrete, as compared tosurrounding areas. This has the dual effect of disguising the crackwithin this line of weakness, as well as managing the long termserviceability of the pavement by ensuring the creation of a pluralityof slab units from the original unitary slab.

[0006] Unfortunately, following the initial crack at the line ofweakness the interfering factor, be it soil or a tree root, willcontinue to affect the slab. The slab, having been broken into discreteand much smaller units, is free to lift. Further, as such interferingfactors inevitably cause differential movement, in that adjacent slabswill be affected to varying degrees, the movement of one slab comparedto an adjacent slab will be at a different rate and displacement.

[0007] The differential movement of one slab to the next will inevitablycause the raising of one peripheral edge higher or lower than itsneighbour. Thus, the once continuous surface will be no longer, withseveral raised discontinuities being formed along the surface.

[0008] Thus, depending on the conditions, the once unitary slab having aflat continuous surface will comprise a plurality of discrete unitsproviding a disjointed and discontinuous surface. Such a surface,instead of providing a convenient path for pedestrian vehicles, such aswheelchairs, prams, etc., will instead become effectively impassable forsuch pedestrian vehicles, not to mention becoming a hazard to foottraffic.

[0009] Thus it becomes a serious issue for Municipalities to devotefunds from constrained budgets to expensive maintenance programmes toreplace the pavements that have suffered differential displacementsbetween the pavement slabs. Further, such Municipalities must maintain acontingent liability against litigation brought by pedestrians who mayinjure themselves by tripping and falling as a result of the raisedperipheral edges of the slab units.

STATEMENT OF THE INVENTION

[0010] It is therefore an object of the invention to reduce differentialdisplacement between concrete slabs, and so diminish the consequentialdetrimental effects associated with this displacement.

[0011] Hence, in a first aspect of the present invention there isprovided an articulation member including a resilient core, said corehaving connection means attached thereto, the connection means adaptedto link two co-planar concrete slabs along an adjacent peripheral edgeof each slab, wherein on application of an out-of-plane displacement toone of the co-planar concrete slabs, the displacement is transmitted tothe other concrete slab through pivoting about the articulation member.

[0012] In a second aspect of the present invention, there is provided amethod of constructing an assembly of articulated slabs, the methodincluding the steps of:

[0013] (i) establishing form-work adapted to receive wet concrete;

[0014] (ii) placing a plurality of articulation members along aplurality of articulation lines;

[0015] (iii) pouring of wet concrete within the form-work so as toengage the articulation members;

[0016] (iv) curing of the concrete, to form a plurality of adjacent slabunits connected by the articulation members.

[0017] In one preferred embodiment of the invention, the wet concretemay fully immerse the articulation members, and consequently form linesof weakness at the articulation lines. In this embodiment, should theassembly be subject to extraneous loads, such as through soil movementor root intrusion, the assembly may crack along the lines of weaknessand so form the plurality of adjacent slab units connected by thearticulation members.

[0018] In a third aspect of the present invention there is provided aconcrete slab, including a plurality of lines of weakness and aplurality of articulation members placed along said line of weaknesswherein said slab is adapted to crack along the lines of weakness,resulting in slab portions that are articulated through connection withthe articulation members.

[0019] In the case of a cast in place pavement, the articulation memberwill be cast within the unitary pavement. By placing the articulationmember along the transverse line of weakness that is typically trowelledinto the pavement when the pavement eventually cracks through theinterference of soil or tree root, the unitary pavement will form twodiscrete slabs adjacent each other, with the adjacent peripheral edgesof each slab essentially co-linear with the articulation member.

[0020] In laying a unitary pavement so as to connect it to an adjacentunitary pavement slab, it is common to place expansion and contractionjoints between said slabs. A contraction joint is typically a resilientsheet of material that on shrinkage of the concrete during curing, theresilient material will prevent voids being created between said slabs.Similarly, and also in application to expansion joints it is known forconcrete slabs to use steel dowels between said slabs. Said dowels areplaced within tubes cast within the concrete so as to permit freeuni-directional movement between the slabs by sliding along the dowels.The dowels being made from steel, and thus being relatively stiff, areplaced to provide a transfer of out-of-plane forces between the slabs.As one slab has a substantial force applied to it, said force istransferred to the next slab by the dowels, and thus maintain acontinuous surface between the slabs. The disadvantage of such a systemis that in transferring this load, localized failure of the concrete atthe peripheral edges of the two slabs must be prevented. Thus, theconcrete portion using the dowels must be specifically reinforced and/orhave a thickened portion designed into the concrete slab. Further, theplacement of the dowels adds a secondary process to the placement of thepavement. Thus while a dowelling system is a useful tool fortransferring displacements and loads between slabs, it is also anexpensive one and usually inappropriate for general applicationfootpaths. This can be seen by the preference of Municipalities forusing on-going maintenance programmes to repair pavements rather thanthe extremely large capital cost of extensive use of a dowelling system.The present invention overcomes the disadvantages of the dowellingsystem by recognizing, firstly, that whilst a continuous surface for apavement is essential, having that continuous surface flat is not so fora footpath. Thus whilst the lifting of a slab unit may not bepreventable within reasonable cost constraints, neither should it benecessary to prevent, so long as the pavement remains serviceable andsafe for pedestrian traffic.

[0021] Thus, it should be appreciated that whilst the articulationmember may not be connected to two slabs in the first instance, butpossibly cast within the unitary pavement slab, the invention commencesfunctioning immediately following the controlled cracking of thepavement and thus the creation of the plurality of slab units. Thisshould not be construed as rejecting the cast of two adjacent slabs,connected by a cast-in-place articulation member.

[0022] As discussed, the outer plane displacement that is applied to aconcrete slab may be caused by tree roots, soil expansion, soil drying,or an unstable base course laid beneath the pavement.

[0023] As the core is resilient, when displacement occurs the slab willlift the articulation member which will flex and pivot relative to thetwo slabs. On further displacement the first slab will lift the secondslab through pivoting about said articulation member.

[0024] The connection means must be capable of transferring the forceassociated with the change of displacement. These forces will includethe mass of the slabs, friction of the second slab as it is lifted fromthe base course, and any cohesive force due to surrounding soil. Thus,the connection means must be capable of resisting, first tensile loadswithin the plane of the slab, then shear forces as the first slab islifted out of the original plane and begins to displace the second slab.

[0025] Preferably the material of the resilient core may include rubber.The pivoting action of the articulation member is central to the coreidea of the invention. Thus in order to achieve the pivoting action aresilient material such as rubber may provide an advantageous effect.

[0026] More preferably, the resilient core material may further includerecycled rubber crumb. The present invention may not require a highdegree of dimensional tolerance in order to function satisfactorily.Thus it may be that the formation of the articulation member is asuitable application of recycled material and thus provide anenvironmental benefit.

[0027] Even more preferably, the connecting means may be made fromrubber also. Thus if the connecting means is also made from rubber thismay provide an opportunity to form the articulation member from a singleunitary extrusion of rubber, and reduce the manufacturing costs of thearticulation member. Alternatively, the connection means may be madefrom a substantially stiffer material than rubber. As the function ofthe connecting means is somewhat different from the resilient core, inthat it must connect to the concrete and transfer loads between theconcrete slabs via the resilient core, it may be that an advantage canbe gained from making the connection means from a different materialthat is economically and functionally more suited to this application.

[0028] More preferably, the connection means may be made from steel. Asdiscussed the connection means may have an economic advantage in beingmade from a stiff material and may be further advantageously made fromsteel.

[0029] Preferably, the connecting means may be projections emanatingfrom the resilient core. Whether the material from which the connectingmeans is made is rubber, steel or any other material, having theconnecting means being projections may be well suited to thearticulation member being placed at the time of pouring the cast inplace pavement.

[0030] Alternatively, the connecting means may be separable projectionswhich may connect with the slab and the resilient core. In oneembodiment of the connecting means being separable projections, theconnecting means may be steel spikes that pass through the core and havea “cog-type” end profile for casting within the concrete.

[0031] Alternatively, the connecting means may be an adhesive material.For instances where the pavement is pre-cast, and so use slabs which aresubsequently laid, the articulation member in order to function, may beadhered to the peripheral edges of adjacent slabs during the pavementlaying.

[0032] Preferably the concrete slabs may be pavement slabs for foottraffic. Alternatively the concrete slabs may be decking for a bridge ormay be slabs for a cosmetic finish to said decking.

[0033] Preferably the articulation members may further include crackpropagation means. Said propagation means are intended to assist in thecontrolled cracking of the slab by providing a line of weakness in thecast in place pavement. Thus, as an alternative to a line of weaknessbeing trowelled into the surface of the concrete, the articulationmember having a crack propagation means may provide the same or similarfunction and advantageously avoid the secondary process of placing theselines of weakness. Alternatively, said crack propagation means mayfurther assist in defining the line of weakness when used with atrowelled surface.

[0034] More preferably, the crack propagation means may be projectionsdirected away from the resilient core towards the upper and/or lowersurface of the concrete, but not penetrating. Thus the thickness ofconcrete between the surfaces and the articulation member will beconsiderably less than that of the surrounding concrete, and thus onapplication of an interfering factor, the concrete will crack preciselyat the required line of weakness and ensure the efficient functioning ofthe present invention. Preferably the articulation means may furtherinclude separation means. The separation means may be projections fromthe resilient core to the upper and/or lower surface of the concrete andactually penetrating said surface. As an alternative to the crackpropagation means, the separation means may be projections that providea dividing barrier between adjacent portions of the pavement, and thusmay separate the pavement into discrete slabs at the time of pouringrather than as a result of cracking. In essence, the separation meansmay be considered transverse formwork which is conveniently placed atthe same time as the articulation member. In addition to the advantagesof controlling the cracking of the pavement and clearly definingadjacent slabs, the separation means may further act as a contractionjoint between the slabs. Thus the articulation member may provide themultiple functions of articulating the slabs, providing contractionjoints to limit gaps in the pavement caused as a result of concreteshrinkage and act as expansion joints to accommodate thermal expansion.

DESCRIPTION OF PREFERRED EMBODIMENT

[0035] It will be convenient to further describe the articulation memberwith respect to the accompanying drawings, which illustrate possiblearrangements of the invention. Other arrangements of the articulationmember are possible and consequently the particularity of theaccompanying drawings is not to be understood as superceding thegenerality of the preceding description of the invention.

[0036]FIG. 1 is an elevation sectional view of the articulation member,according to the present invention.

[0037]FIG. 2 is an elevation sectional view of the articulation member,according to another embodiment of the present invention.

[0038]FIG. 3 is a further elevation sectional view of the articulationmember, according to the present invention.

[0039]FIG. 4 is a further elevation sectional view of the articulationmember, according to another embodiment of the present invention.

[0040]FIG. 5A is an elevation view of the support means, according toone embodiment of the present invention.

[0041]FIG. 5B is a plan view of the support means according to FIG. 5A.

[0042]FIG. 6 is an elevation sectional view of the articulation memberaccording to a further embodiment of the present invention.

[0043]FIG. 1 shows the articulation member (1) cast within a pavement.The articulation member (1) includes a core (2) about which thearticulation member (1) can pivot. Further included are the connectionmeans (3), in this case sideways projecting portions of sufficient sizeto engage the concrete (5, 6), and transfer loads from one side of thearticulation member (1) to the other.

[0044] In this embodiment of the invention the articulation member (1)is made from a single elastomeric extrusion, such as rubber, which mayalso include a proportion of, or possibly entirely from, recycled rubbercrumb. The environmental benefits of being able to use recycled rubbercrumb from granulated car tyres will be clear.

[0045] It will be clear to the person skilled in the art that the core(2) can incorporate a portion of the articulation member (1), that is ofa thicker section than the connection means (3), or be of the same size.In defining the portion of the core (2) rather than purely geometricdescription, it is important to recognize that the core (2) is thatportion of the articulation member (1) that is subjected to the greatestflexural stress as load is transferred between adjacent slabs (5 and 6).In placing a stress based functionality to the articulation member (1)the connection means provide, in terms of stress, an engagement with theconcrete which may be achieved through pure friction, or through amechanical jointing with the concrete (not shown), and thus at least fora frictional engagement the primary consideration is one of maximizingsurface area without unduly reducing the thickness of the concretepavement above and below the connection means (3). The core (2) however,is required to transfer load from one pavement to the next through thetransfer of flexural stress and thus, in terms of geometry need only beof a size to handle the expected flexural load, the most significantportion being the tensile load in the upper portion of the core (2).

[0046] Also included are the crack propagation means (4), in this caseupwardly and downwardly directed projections, which create a concretesection of reduced thickness, and thus promote cracking of the concreteat that point.

[0047] On cracking, the pavement is effectively divided into two slabunits 5 and 6, which without the articulation member (1) wouldeffectively act independently of each other. Having the articulationmember (1) in place, however, provides for the transfer of displacementand load from one slab unit (5) to the next (6).

[0048] Finally, as is typically done for such pavements, a trowellednotch (7) is placed transversely across the pavement, so as to furtherreduce the section thickness of the concrete, and so promote theformation of a crack. Whilst this may be standard practice without theinstallation of the articulation member (1), it can become notionallysuperfluous, from a functional standard point to include such a notch(7) when using an articulation member (1) having the crack propagationmeans (4). Nevertheless, in certain circumstances, the addition of sucha feature, can provide an aesthetic benefit by hiding the crack from thepavement users.

[0049]FIG. 2 shows another embodiment of the articulation member (1),having separation means (8). As an alternative to using crackpropagation means (4), the articulation member (1) may incorporateprojections upwardly, and possible downwardly from the core (2), suchthat a divide is placed within the pavement (5, 6). Thus, the slab units(5 and 6) are defined prior to pouring, without having to rely on acrack forming first. Among the benefits provided by the inclusion of theseparation means (8) is the saving in expansion joints. Thus, whilstexpansion joints may be provided for pavements, so as to accommodateconcrete shrinkage during curing, the separation means (8) provides afull thickness buffer between the slab units (5 and 6), which may limitthe formation of gaps in the pavement due to shrinkage.

[0050]FIG. 3 shows the articulation member (1) of FIG. 1 following theapplication of a severe displacement to slab unit (6), caused by a treeroot (9). As pavements for pedestrian traffic are commonly placed inproximity to trees, it is common for a root (9) to extend underneath thepavement (6). As the tree grows, so does the root (9), the consequencebeing uplift of the pavement (6). Without he installation of thearticulation member (1), slab unit (6) would be displaced upwards,independent of slab unit (5). Thus, a discontinuity in the pavementwould be created as a result of the step the effected of slab unit (6).Not only does this cause a problem for vehicles permitted access topedestrian pavements, but also becomes a hazard for foot traffic, wherea user may trip and fall.

[0051] By including the articulation member (1), slab unit (5) is alsodisplaced upwards to maintain the relatively continuous surface of thepavement. Whilst a crack (10) may form, detritus along the pavement, oreven a maintenance programme of filling such a crack, is all that isrequired to eliminate any serviceability or aesthetic problems which maybe caused. If such remedial action is required, this is minor incomparison to the maintenance cost to replace such pavements.

[0052] In consideration of the connection means (3), there may be anumber of useful profiles of the concrete engaging end of the connectionmeans (3) can adopt. It should be noted that this discussion is basedentirely on the cast-in-place situation, where the articulation member(1) is placed prior to the pouring of the concrete, and thus thearticulation member (1) becomes integral with the concrete. Analternative to this is the use of pre-cast slabs, where the connectionmeans may include an adhesive, or other engaging means, to connect withthe pre-cast slabs.

[0053]FIGS. 4, 5A and 5B show a support means (12) which is used toassist in the placement of the articulation member (1). In somecircumstances it may be advantageous to hold the articulation member (1)in place during the pouring of the concrete in order to form thepavement. In certain circumstances, because the specific gravity ofrubber is such that the articulation member (1) may float in the denserconcrete (typical specific gravity of 2.2 to 2.4) it may be advantageousto have a bracket which when connected to the form-work (16) can resistthe floatation of the articulation member (1) as the concrete approachesand amerces the connection means (3). Therefore, in one embodiment ofthe invention, there is provided a support means (12) comprising anassembly of angle members (14A, 14B and 17). Member (17) is fixed to theform-work (16) through nails (13). Further elements (14A and 14B) arefixed to the angle (17) and are oriented so as to run parallel to thedirection of the articulation member (1). Members (14A and 14B) areoriented so as to provide a close fitting gap into which the upperseparation means (4) can slide with the fit such that the members (14Aand 14B) once engaged with the articulation member (1) will enclose theupper portion of the separation means (4) and bear down upon theconnection means (3). Thus, is the fully installed condition, thesupport means will comfortably engage the articulation member (1) readyfor the pour of concrete. The degree to which the support means (12) isrequired will depend upon a number of factors, and so the level ofconcrete at which the support means (12) is no longer required may be ata point (15A), and thus just up to the connection means (3), or to apoint (15B) where the concrete has amerced the connection means (3). Ineither case and as determined by those installing the articulationmember (1), once the articulation member (1) is securely engaged withthe concrete, the support means (12) may be removed and the concretepour continued.

[0054]FIG. 6 shows an alternative arrangement of the support means (19),which is used as a means to finish a portion of a pavement (5), butwhere it is expected that further work is required, and so thearticulation member (1) is used as a terminating barrier, ready forfurther additions to the pavement to be added. The support means (19)includes parallel members oriented so as to enclose the connection means(3) on the side of the articulation member (1), to which the futurepavement will be added. A lower member (18B) is placed abutting thelower portion (4B) of the separation means and the connection means (3),and a further member (18A) placed abutting the upper portion (4A) of theseparation means (4), and the opposing side of connection means (3).These members are fixed to the form-work (16) through nailing aconnecting bracket (20) which is fixed to the supporting elements (18Aand 18B).

[0055] Thus, on completion of a portion of the pavement (5) there willbe projecting from that portion an articulation member (1) having aprotruding connection means (3) which is supported and confined by thesupport means (19), which is subsequently fixed to the form-work (16).

The claims defining the invention are as follows:
 1. An articulationmember including a resilient core, said core having connection meansattached thereto, the connection means adapted to link two co-planarconcrete slabs along an adjacent peripheral edge of each slab, whereinon application of an out-of-plane displacement to one of the co-planarconcrete slabs, the displacement is transmitted to the other concreteslab through pivoting about the articulation member.
 2. The articulationmember according to claim 1, wherein the material of the resilient corematerial includes rubber.
 3. The articulation member according to claim1 or 2, wherein the resilient core material includes recycled rubbercrumb.
 4. The articulation member according to claims 2 or 3, whereinthe connecting means, at least partially, is made from rubber.
 5. Thearticulation member according to any one of claims 1 to 3, wherein theconnection means, at least partially, is made from a non-resilientmaterial.
 6. The articulation member according to claim 5, wherein thenon-resilient material includes a metallic portion.
 7. The articulationmember according to any one of the preceding claims, wherein theconnecting means is integral with the resilient core.
 8. Thearticulation member according to any one of claims 1 to 6, wherein theconnecting means are mountable on the resilient core.
 9. Thearticulation member according to claims 5 or 6, wherein the connectingmeans are metallic spikes passing through the resilient core.
 10. Thearticulation member according to claims 5, 6 or 9, wherein theconnecting means have a cog-type profile at terminal ends of saidconnecting means distal from the resilient core.
 11. The articulationmember according to any one of claims 1 to 5, wherein the connectingmeans includes an adhesive surface adapted to adhere to the peripheraledges of adjacent slabs.
 12. The articulation member according to anyone of the preceding claims, wherein the concrete slabs are pavementslabs for foot traffic.
 13. The articulation member according to any oneof claims 1 to 11, wherein the concrete slabs are decking slabs for abridge.
 14. The articulation member according to any one of thepreceding claims, wherein the articulation member further includes crackpropagation means.
 15. The articulation member according to claim 14,wherein the crack propagation means includes at least one projectiondirected towards a top surface of the slab.
 16. The articulation memberaccording to claim 15, wherein the crack propagation means furtherincludes at least one projection directed towards a bottom surface ofthe slab.
 17. The articulation member according to any one of claims 1to 13, wherein the articulation member further includes separation meansfor providing a barrier between adjacent slabs.
 18. The articulationmember according to claim 17, wherein the separation means are at leasttwo projections emanating from the resilient core, and extending to orbeyond an upper and lower surface of the slabs.
 19. The articulationmember according to claim 17 or 18, wherein a cross-sectional shape ofthe articulation member is substantially cross-shaped with theconnecting means directed in a horizontal plane, and the separationmeans directed in a vertical plane.
 20. The articulation memberaccording to claim 19, wherein the separation means and connecting meansintersect at the respective mid-points of the separation means andconnecting means.
 21. A method of constructing an assembly ofarticulated slabs, the method including the steps of: (i) establishingform-work adapted to receive wet concrete; (ii) placing a plurality ofarticulation members along a plurality of articulation lines; (iii)pouring of wet concrete within the form-work so as to engage thearticulation members; (iv) curing of the concrete to form a plurality ofadjacent slab units connected by the articulation members.
 22. Themethod of constructing a concrete slab according to claim 21, whereinsaid articulation member is the articulation member according to any oneof claims 1 to
 20. 23. The method of constructing a concrete slabaccording to claim 21 or 22, wherein step (ii) further includesplacement of support means, said support means adapted to engage, atleast one, articulation member during the pouring step.
 24. The methodof constructing a concrete slab according to claim 23, wherein thesupport means includes an assembly of members adapted to connectdirectly to the form-work so as to engage the, at least one articulationmember so that the articulation member is maintained in a desiredconfiguration and position during the pouring step.
 25. The method ofconstructing a concrete slab according to claim 23 wherein the supportmeans engages the at least one articulation member by encompassing anupper portion of the separation means and engaging the connection meansso as to prevent uplift of the articulation member.
 26. A concrete slab,including a plurality of lines of weakness and a plurality ofarticulation members placed along said line of weakness wherein saidslab is adapted to crack along the lines of weakness, resulting in slabportions that are articulated through connection with the articulationmembers.
 27. The concrete slab according to claim 26, wherein thearticulation member is the articulation member according to any one ofclaims 1 to 20.